The invention relates to an antifriction bearing with a sensor for speed or acceleration of the wheels or for driving or braking forces, wherein the sensor includes a microsensor.
Many antifriction bearings with sensors are known. For instance, DE 37 35 070 A1 shows an antifriction bearing with a pulse ring to record its rotational speed. EP 0 432 122 A3 shows a wheel bearing for motor vehicles with a load sensing device. DE 42 39 828 A1 discloses a hub and bearing arrangement with an integrated rotational sensor and temperature measurement.
For actively stabilizing a vehicle like a car, a large number of parameters should be recorded, which describe the momentary status of the vehicle and are used as input parameters for control systems. Measuring directly measurable variables is advantageous. These variables include braking and driving forces, i.e., lateral forces, the rotational speed of the wheels, the angular acceleration and lateral forces acting on the chassis. Owing to the transmission of force from the road to the chassis of the vehicle, the wheel bearing provides an ideal measuring point for recording forces and accelerations. Measuring the angular acceleration on the rotating part and measuring the lateral acceleration given by driving or braking operations permits indirect determination of slip, one of the main measurement variables in the antilock brake system, antislip control and dynamic vehicle stabilizing.
A sensor system provided for measuring these variables can be integrated in the wheel bearings both of the driven wheels and of the non-driven wheels and can be installed in the car as an intelligent subsystem.
Within antilock brake systems or antislip control systems, passive or active sensors are currently being used as sensory components to measure the rotational speed of the wheels. Furthermore, future integrated cost effective sensors are provided for recording the yaw moment (see Elektronik Journal 13/1995 pages 34 and 36), the yaw moment occurring during a skidding operation being compared with the steering-wheel angle.
It has previously only been possible to record accumulated loads, for example, forces in the wheel bearing and the friction value between the tires and road surface, directly with the aid of expensive measuring systems which are used on prototypes.
For example, a multicomponent wheel hub records forces and moments by applying a relatively complex and expensive strain gage in conjunction with complex signal processing and transmission of measured values. A so-called measurement wheel system is known, which also uses strain gages to measure the forces occurring in the wheel bearing indirectly by means of load cells.
Other measuring systems permit the friction value between the tires and the road surface to be measured by very small permanent magnets vulcanized into the tire, and the change in the magnetic field caused by the braking or acceleration operation is detected by Hall sensors.
A high degree of complexity and thus high costs are common to all the systems, thus ruling out their application as a mass product.